Physics Paper 1 COSMOLOGY

• Astronomical unit

  The average distance from the sun to the earth, about 150 million kilometers or 1.5 times 10 to the power of 11 meters
• Light year

  The distance traveled by light in one year, 9.5 times 10 to the power of 15 meters
• Arc minute

  One sixtieth of a degree
• Arc second

  One sixtieth of an arc minute, one over three thousand six hundredth of a degree
• Parallax

  A technique used to determine the distances to nearby stars by measuring the apparent shift in position of a star against the background of distant stars
• Parsec

  The distance at which one astronomical unit subtends a parallax angle of one arc second, approximately 3.1 times 10 to the power of 16 meters
• The cosmological principle states that the universe is both isotropic and homogeneous, and the laws of physics are universal
• Doppler shift equation

  Delta lambda over lambda = v/c, or delta f over f = v/c, where delta lambda is the change in wavelength, lambda is the original wavelength, v is the recession speed, and c is the speed of light
• Hubble's law

  The recession speed of a distant galaxy is directly proportional to its distance from the Earth
• Converting Hubble's constant to SI units

  Hubble's constant in km/s/Mpc needs to be converted to s^-1 by dividing by the conversion factor of 1 Mpc = 3.1 x 10^16 m
• The age of the universe is approximately 14 billion years
• Big Bang theory

  Time and space created at the Big Bang

  2. Rapid expansion (inflation) in the first 10^-35 seconds

  3. Fundamental particles gain mass at 10^-6 seconds

  4. Atoms form at 380,000 years, releasing cosmic microwave background radiation
• Dark matter

  Exotic, unobservable matter that interacts gravitationally, explaining the observed higher rotation speeds of galaxies
• Dark energy

  The energy of empty space that seems to fuel the expansion of the universe